Balancing device for rotary cutting tools

ABSTRACT

A device is provided to eliminate unbalance and vibration occurring due to nonsymmetrical mounting of rotatable tools and tool holders in milling machines, arboring machines, drilling machines, etc. Attached to the tool holder in an appropriate place is a weight support able to receive one or more appropriately sized weights. The weights being radially adjustably securable to the weight support.

P BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates to the area of cutting and machining and moreparticularly to milling tools and the like intended to be fixed at atool holder for inside machining of a work piece and preferably forcutting tools including a holder device displaceably arranged relativelyto the axis of rotation.

2. Description of the Prior Art

Tools and arrangements of the kind mentioned above having the positionof the tool or the tool holder radially offset and thereby unbalancedexist in connection with various cutting techniques, especially inmilling or arboring machines and the like where a rotatable tool holdercarries a tool and the tool is fastened in such a way that the center ofgravity will be offset from the axis of rotation. In slowly turningmachines, the relatively small weight of the tool has no negativeinfluence on the machine as a whole. In the majority of cases, two toolsare used and allowed to balance each other.

In high speed machines of the kind used more and more today andespecially in machines having one single tool, problems arise. Many suchmachines are placed on shoes or pads, i.e. fasteners having vibrationdampings bodies of rubber or similar material, and it has been foundthat, if an unbalanced tool is used in such a machine, the whole machinemay start vibrating which can negatively effect the resulting work. As aconsequence, the user may have to refrain from utilizing the machine athigh speed.

Earlier double or triple mounted tools cannot be used in precisionmachining where it is intended to use cutting inserts of the types mostin demand today as such tools would require complicated relativeadjustment. It is also not possible to use standard inserts and toolholders for double mounting arrangements and the result will be that thespeed must be kept low if vibration is to be avoided and standard partsare to be used.

An object of the present invention is to bring about an arrangementeliminating the above mentioned drawbacks resulting from nonsymmetricalmounting of rotating tools and tool holders in milling machines,arboring machines, drilling machines and the like and making it possibleto use in a practical way replaceable inserts of modern design whichallow high yield and simultaneously give a high quality result.

SUMMARY OF THE INVENTION

In a milling spindle or shaft of the milling head and tool holder thevibration problems occur because the tool with its cutting insert arenot correctly balanced in radial direction. The vibrations and unbalancebring the whole machine into a state of resonance vibration and this ismore prevalent if the machine is supported by elastic pads. If themachine is firmly secured by bolts directly to the foundation or to afloor, the vibrations may seem to be less intense but the machinenevertheless will be affected negatively. Additionally, there may bediscomfort for the operator.

According to the invention, the problem is solved by attaching to thetool holder in an appropriate position a carrier means adapted toreceive one or more weights of appropriate sizes and by arranging theweight or weights to be radially adjustably attachable to the weightcarrier means.

BRIEF DESCRIPTION OF THE DRAWING

One embodiment of the device according to the invention will bedescribed with reference to the attached drawing, in which:

FIG. 1 is a side elevational view showing a portion of a tool holder tobe attached to a milling machine shaft, said holder presenting thedevice according to the invention,

FIGS. 2 and 3 are a longitudinal sectional view and an end view,respectively, of a weight holder used in the present invention, and

FIG. 4 is a longitudinal sectional view of a weight.

DETAILED DESCRIPTION OF THE INVENTION

A tool holder part 1 has an end face 2 presenting a recess 3 forreceiving a wedge (not shown) adapted to fit into and be secured tocorresponding details of a machine (not shown), i.e. an end millingarbor or the like. The tool holder part 1 includes an inner portion 4and an outer portion 5 which by means of a slide guide 6 and by a screwdevice (not shown) is radially displaceable relatively to the innerportion 4.

At the outer portion 5 of the tool holder part 1, there areappropriately arranged abutments and clamping means for a tool holder(not shown). By using single tool holders projecting more or less in theone radial direction only, there will occur at the outer portion 5 anunbalance which on rotation naturally also vibrates the tool holderpart 1. As different machining operations demand different radialsettings and further, during the course of such operations, for examplein internal turning, the tool holder with the tool will be displacedradially outwardly resulting in different degrees of unbalance. Byattaching tools having different weights in different radial positions,the center of gravity will be moved more or less away from the axis R ofrotation.

According to the invention, on the tool holder, at least on one sidethereof and preferably on the side opposite the side towards any radialdisplacement, there is an attachment seat for a weight holder arrangedfor receiving and securing weights in different positions.

As shown in FIG. 1, the outer part 5 of the tool holder has a threadedbore 16 which receives a threaded end portion 7 (FIG. 2) of a hollowshaft 8 having a head 9 with a wrench attachment. Referring again toFIG. 1, one or more weights 10 may be fastened to the shaft 8 accordingto the balancing requirements. Each weight has a body having a throughbore 11 (FIG. 4) and also a lateral threaded bore for a stop screw 12(FIG. 1).

The size or weight of each weight 10 may be determined by the balancingrequirements. Alternatively, instead of a one piece body 10, severalthin washers or rings in sets together can cover a wide range ofweights. By making the weight or weights displaceable and affixable indifferent positions, a very good adaptability is achieved for differentbalancing requirements. In FIG. 1 of the drawing, the weight 10 is shownits inner most position and it is displaceable from this position to anyposition as far as the head 9 of the shaft 8 and each such positionresults in a different balancing value.

The invention is not limited to the embodiment shown above but can bevaried within the framework of the following patent claims.

What is claimed is:
 1. A balancing device for a rotatable tool holderwhere a tool is attachable in different radial positions relatively toan axis of rotation of the tool holder thereby causing an unbalance,comprising:(a) support means positioned in a predominant direction ofradial displacement of the tool and adapted to receive at least oneradially adjustable weight, said support means includes an elongatedshaft threaded into and extending from a radial bore in the tool holderin an outer part thereof radially movable relatively to an inner part,said elongated shaft having an outer head; and (b) at least one weightradially adjustably secured to said elongated shaft.
 2. The balancingdevice according to claim 1, wherein each of said at least one weighthas a positioning and locking screw to engage said elongated shaft. 3.The balancing device according to claim 1, wherein said at least oneweight is a plurality of ring like elements of which at least some havemeans for securing themselves on said elongated shaft.
 4. The balancingdevice according to claim 1, wherein said at least one weight has acylindrical shape.